So the USB adaptor does the conversion to OBD2 KL protocol. Here you can see Power and GND (4, 5, 16) are populated and pin 7 (K) pin 15 (L). This has a wire inside that shorts pins 17 and 20, and connects them to 7. Since you will probably want the full suite of modules I N P A software offers, you need a £6 BMW to OBD2 adaptor. I bought a £12 USB OBD2 adaptor (FTDI prolific based is mandatory and also common). Handily both K lines can be shorted to get a simple OBD2 K USB adaptor to work. If you want the ABS, Airbag or anything else, you need the 12V, GND, and both K lines found on the round connector. If you want to talk to the engine and gearbox you only need the 12V, GND and K line found on the 16 pin connector. The car in this case is a 1999 and has both the 20 pin and 16 pin OBD diagnostics. One for the engine and Gearbox, the other for everything else. It's called the KKL since there are 2 K lines.

With the ignition on, the L Line is not needed, since the modules are already awake. As such the BMW is not dierctly compatible with RS232, either in baud or signalling levels, and could damage your PC's RS232 port if directly connected. L line is some sort of RTS/DTS line that wakes up the modules on older cars. The K line is a bi-directional serial bus with a 10.4kbaud data rate. Here is my write up for communicating with my BMW using cheap USB interfaces.īMW uses a KKL system.

Inpa bmw e38